This invention relates to a hydraulic power-steering system for vehicles comprising hydraulic directional control mechanism between the input and output shafts of the steering shaft of a vehicle.
In a conventional system of this type, as illustrated in FIG. 3, an input shaft 103 is connected, through a torsion bar 102, to a rotor 101 formed integrally with an output shaft 100. A spool valve 104 is shifted either right or left from the neutral position, depending on the angle formed by relative rotation of the input and output shafts 103 and 100. By the shifting of the spool valve 104, hydraulic working fluid, which is usually introduced through a fluid-supply port 105 and discharged through a return port 106, is supplied to the steering power cylinder through either of output fluid passages 107 and 108.
However, in such a system, the working fluid shifted by the spool valve 104 is introduced to the steering power cylinder through a pressure-oil chamber 109 that is kept in contact with an end surface of the rotor 101. Due to this structure, thrust is exerted on the rotor 101 when the pressure in the pressure-oil chamber 109 becomes high. Here arises a problem that a thrust bearing 110 must be provided to receive reaction working on the rotor 101.
Also, since the pressure-oil chamber 109 lies at an intermediate point of the output fluid passage 107, the rotor 101 cannot readily be separated from the output shaft 100. This results in difficult assembling and disassembling, and higher manufacture cost.
Further, the conventional power-steering system, in general, necessitates providing a stopper pin to restrict the relative rotation of the input and output shafts in a limited space, which makes the construction of the system complex. As a consequence, the system becomes less strong as well as more difficult to manufacture.